I was thinking of a hotel sesh soon, with the options of instant potatoes, cake batter, or pancake batter, just mixed with water to make a sludge I'll wallow in for a while. Afterwards, are those safe to dilute with a lot of water and go down the drain?

The clue is in the phrase 'lot of water'. If you really dilute it a lot, you should have no problem.

Put it down the toilet. The toilet takes all your shit without blocking so a few buckets of batter really won't be an issue.

When I'm doing disposal; I half fill a bucket and top with water. Then I swish my hand through it to break the mess into floating lumps. The result then flows freely like water and has never caused me any issues with blocked pipes etc.

Bathtub drains can deal with it too, but the plughole acts as a sieve and blocks pretty easily unless you can dissolve it in water or get the lumps small enough to go through.

What you don't know is what else is already down that drain. If the drain has a lot of hair, for example, then you are much more likely to have a problem with anything thick. Or someone who played before you and used clay, and the clay has clogged up half the drain. Hotel drains might be fine, or they might have decades of junk clogged up in there.

As was said earlier, the toilet is a better bet for cleaning out. You can line the bathtub with plastic sheeting to make it easier to collect everything. Then you can put it down the toilet, a "load" at a time. You can also then gather the sheeting and put it into trash bags to remove.

Also, consider if you are on a septic or public sewer. This has a huge impact on what you should/shouldn't put down a drain regardless on how you send it down.