So, say if I was going to fill one of those 5 gallon work buckets you see in construction supply stores with cake batter (less of a hypothetical situation and more of an inevitable one). Does anyone have a rough idea of how many boxes of cake mix I'll need to buy in order to do a decent job of filling it? Also, can I substitute water for milk when mixing the batter and still get the same consistency?

About 10-12 boxes, depending on how much water you mix in. The only cake mixes I ever find already have powdered milk in them- just add water...and I'll add 1 egg per box as well. Also, if you plan on lifting the bucket above someone's head, be aware that a full bucket will be VERY heavy!

I used 10 boxes in a session once and it filled just over half of one of those buckets with a pretty thick consistency. I almost always use hot water when mixing, so I can't really compare how that works versus milk, but if you do end up using like 15-20 boxes (if you really wanted it almost actually full) then it would obviously be much more cost effective just using water.

Add the water gradually to the cake mix, not the other way round. This should avoid lumps.

those proctor silex or however you spell it products are garbage. if you ever want to make anything THICK and change consistencies at all....if you already have a drill all you have to get is a paint mixer bit for it and it costs like 5 bucks and makes it go by WAY FASTER. add water first, then the mix and watch it go!! so you will have super warm batter! use hot water!

1 gallon = oz

cake mix is usually around 16 oz

add 2 cups of water, 16 oz each.

That's about* 48 oz per gallon.

About 2.5 boxes per gallon.

For a 5 gallon bucket, 2.5x5 gets you about 13.

*Note: cake mix is dry ounces, water is fluid ounces. The two aren't exactly the same, but for the purposes of estimation, a good place to start. YMMV

My profile picture is a 5 gallon bucket. You can see its mostly full. That's 14 boxes. But I also like it just barely pour-able. Like, just beyond the point where you would really have to scrape it out.

Excellent tips. Thanks, everybody.

Related question: how well does pudding mix work if you use water instead of milk, especially if its being used for a pie filling?

A couple of other important things:

1] most cake batter mixes call for oil...this will help you control the viscosity and smoothness of the batter (and may substitute in some mixes for eggs -- but the egg has other effects on the batter's consistency/texture...one should experiement with smaller amounts of batter before going "full gunge")

2] Remember that cake mix has baking powder in it (!!) and baking powder stings the eyes...so be prepared with paper towels to wipe the model's eyes should batter make contact with them.

3] Yes, use HOT water...so that the batter is warm when it's eventually used (don't wait too long, after adding the hot water, like no more than 20-25 minutes)...this will please your model immensely as it will enhance the sensual nature of the experience (clothed or nude)

if you want it to look like this then add shortening (or cake margarine) and eggs first then hot water to make the right consistency

Let's say I'm using a hotel bathtub for this.....keep the plug in until finished and fill the tub with hot water....it will go down the drain easily? Or I should wrap it in plastic and let the maid wonder what went down? Possibly bring an oven and bake a cake for my co-workers?

If you use the bath, like we do, make sure the subject stays seated or lying down and DON'T try and wash it down the plug hole. We tried that and one industrial plunger and about 4 hours later :-(
I keep filling the bucket and pour it in the toilet, continuously flushing.
That way if you have to call a plumber you can always explain the brown slop in the bath, the walls and the toilet down to a dodgy curry and a dose of the "salts"
When he says "Salts?"
You tell him - "yes, somersaults"

pudding mix will only mix with milk. DO NOT MAKE THAT MISTAKE!!!

I've been experimenting with making my own cake batter from scratch -- white flour, oil, sugar, water. Buy the big bulk bags of the stuff and cheap canola oil and it's a real $$$ saver in my experience. There are recipes online you can look up or just experiment like I did until you get the right consistency. My last session went great -- no dairy, no baking powder/soda, no eggs (add that stuff if you really *want* it, of course).

I put the bucket in my kitchen sink and let water flow into it continuously, mix it around from time to time so it thins out and run the garbage disposal while doing this in spurts. Seemed to work fine.