Two taps better than one
You have mentioned in the past that having twin take-offs from a single tank allows you to fit two separate regulator first stages. Surely this cant provide proper redundancy, because if you have trouble with a free-flow on one regulator, you cant turn off the tank without losing the gas supply to the other.

width=100% width=100%
The pointless approach to twin take-offs from a single cylinder; and the sensible - each has its own tank-valve.

Thanks to the modular tank valves available today, you can contrive to fit two regulators to one. This is pointless because, as you rightly say, if you turn off the supply to one, you turn it off to the other.
However, by fitting two take-offs with separate tank-valves, each supply is totally independent. These twin-valves are often known as Y-valves or H-valves, depending on their configuration, and they are a common sight among diving instructors in Continental Europe, where they use a single tank but with two separate regulators.
This works exactly like a manifolded twin-set, but witha single tank. An isolation manifold is not needed, as there is only one tank.
A 15-litre tank can be used exactly like a 12-litre tank and a 3-litre pony, except that there is only one reservoir of gas, and no error can be made by the diver breathing from the pony in mistake for the main supply.
Of course, you still have to manage your gas supply properly.

width=100% Two types of drysuit connectors
Two hoses
I borrowed a drysuit from a friend who asked what hose connection I had. Arent they all the same

Two different connections are commonly encountered on drysuit inflation valves, but gradually the straight-edged connection nipple, which is interchangeable with the one on your BC direct-feed, is taking over from the older and once very common waisted nipple. Unfortunately, you need to have a matching hose connection.

width=100% lone pressure gauge or bulky console
Console or wrist
I am new to diving and would like to know whether its better to have a console

A better way to look at the choice is to ask yourself if you want all your instruments mounted in one place, or whether you would prefer to have your compass and depth-gauge/computer elsewhere.
Its a matter of personal choice, but I prefer to have my computer on my wrist where I can glance at it instinctively, and my compass on the end of a lanyard in my pocket, so that I can pull it out and use it easily when held out in front of me.
Putting everything together on a console is a seductive idea, but it means reaching for and lifting the bulky console every time you want to read a gauge.
On the other hand, a solitary little pressure gauge can be threaded up through the waistband of a BC so that it too can be seen at a glance.

Neoprene rash
I seem to be allergic to neoprene - I come out in a rash. Is it possible to buy suit, boots and gloves that do not use this material

We have had one or two letters regarding this, and presume that you are not drysuit-diving, when a membrane suit might be the answer. You might try a lightweight membrane drysuit such as the Whites Fusion, which is suitable for use in tropical water. Otherwise, its a matter of separating your skin from the offending material.
Try wearing a natural Merino wool long-sleeved vest and long pants from Icebreaker under your wetsuit, or recycled synthetic underwear of the type bearing the Patagonia brand.
I always wear ordinary nylon socks under my wetsuit boots, and find that although I dont have an allergy, my feet dont suffer the abrasions I see on others after a lot of time in the water.
It is possible to buy sailing gloves or even gardening gloves in a heavy canvas. These will not insulate your hands, but will protect them when wreck diving. Woolly liner gloves normally used under dry gloves will work with wetsuit gloves, too.
You can get a lightweight hood in a modern flexible plastic, or a Weezle hood-liner that you can wear under the warm neoprene one.

My leaky masks
I am a small fella, and have always suffered from leaky masks, I always do the obvious, like making sure that my hair is very short. I have tried several masks, which gets expensive as they need lenses, so they cost £100 a time! Any suggestions would be much appreciated.

We are surprised, because when we did our last mask comparison even my eight-year-old daughter successfully used all but a couple of the masks tested, and Im sure she would have a smaller face and longer hair than you!
There are small masks available - check at your local dive shop. Modern soft silicone skirts are very forgiving, and unless your face is unusually deeply lined, you should in theory have no difficulty.
I have both a face that shows my age plus facial hair, but rarely have a problem that is not of my own making.
You are probably unconsciously exhaling through your nose, which displaces the mask skirt and lets a trickle of water back in the other way.
Dont have your mask strap so tight that it distorts the frame.

width=100% Clearing water from the ear pockets of the Pro Ear mask - its easy
Keeping ears dry
With regard to the ProEar2000 mask that encloses the ears, most clubs train divers to fit masks under water, and my club also has a training drill that involves the swapping of masks in open water, and at depth. This training is not compulsory for all, but some knowledge of mask-clearing must be essential - you cant surface every time your mask floods. So what happens with this type of mask when the ears get wet due to the mask being knocked off, either by another divers fins, rope tangle, kelp or other unforeseen obstructions

The IST Pro Ear2000 mask is unique in that it has flexible tubes with one-way valves that connect the ear pockets to the main section.
When you clear water from the mask by blowing air from the nose into it, the ear pockets are cleared too. Its that simple!

Auto-dump trouble
How can auto-dumps not work Reading around, they get blamed fairly regularly for uncontrolled ascents.

The function of an auto-dump is to keep a drysuit at constant volume as the air within it expands during the decreasing pressure of an ascent. It does this by employing a spring that opens only when the air pressure exceeds the springs ability to hold the valve shut.
The auto-dump is adjustable to suit personal needs and can be screwed completely shut.
If you are correctly weighted for neutral buoyancy just under the surface with no air in your suit, youll be amazed how little you need to add on a descent. However, many divers do not appreciate this, and wear too much lead.
This leads to them putting more air into the suit. This air must be allowed to escape gradually on the way back up.
Auto-dumps do not allow a rush of air to pass through them, and a bulky undersuit can block the internal pathway of the air too, especially if large amounts of air have to counteract the effects of the lead used by an over-weighted diver. So its not the auto-dump, but bad technique, that leads to uncontrolled ascents.

Air in a nitrox tank
I have a tank that has been nitrox-cleaned but I want to use air. What do I need to do

The reason a tank is cleaned for nitrox use is that for the purpose of partial-pressure blending (a popular method in the UK) pure oxygen must be added first.
Handling pure O2 can be hazardous in the presence of hydrocarbons, so this is done for the safety of the nitrox-blender and his installation as much as anything else. The tank is then topped up with air.
This air is double-filtered to avoid any moisture getting into the tank, and the disastrous consequences of corrosion causing oxidisation or rust through those high levels of oxygen.
If you want to use air but keep your tank nitrox-clean, simply specify that any air is double-filtered as it would be for a nitrox fill. Nitrox suppliers have to take on trust that the owner of a nitrox tank has kept it nitrox-clean during the interval between statutory inspections.
Where de-nitrogenised air is used to make nitrox, as with the membrane system typically used throughout those parts of the world where vast amounts of nitrox are used, tanks in normal condition suffice.