It's possible to have a messy time in a hotel. I've done it many times, mostly in the bathtub/shower. You just need to plan well and be organised and careful.
You have to think about how you get the stuff in and out and past receptionists without looking to suspicious. A really big suitcase or rucksack is handy for this. You can then get all your rubbish and dirty/wet clothes back in it (don't forget to bring plenty of big, quality bin bags).
As has already been said, it's best to use stuff that's easy to dispose of down the plug or toilet. So smooth stuff is better than lumpy. You might be able to get it down the plughole but you don;t want to clog the pipes. You can bring in powdered gunge stuff to mix up, but you'll then need to also bring in buckets to mix the stuff up in. That's fine if you've got a big enough bag.
I use cheap plastic DIY dust sheets on the floor to catch the worst of any splashes. They're not really strong enough to do a whole session on but work well for containing any accidental splashes. They can then be easily rolled up and thrown away. You can use your won sheets or towels on the floor too but they're a lot bulkier especially when wet and gunky. Bring your own towel or two for drying yourslef after you've showered as hotel towels are always bright white and there's always a bit of bright goo you miss!
A big carwash sponge is a good idea to pack for washing yourself and the walls etc.
Have had a few hotel meets, though it's been a while. If you are playing with someone you have not met before, insist on a pre-meet first a few days beforehand. A no-show is always a bummer but if you've paid for a hotel room for nothing that can only make things worse. Book a room in a large chain hotel where you will not attract unwanted attention - nowhere too posh that might send you a large bill if you miss something during the cleanup. Some people recommend booking a disabled room as the bathroom is larger, although I have not done that myself. If you need to be anonymous / make sure a partner doesn't find out, either get the other person to book the room and pay your share in cash on the day or make sure you tick every box you can find for no marketing etc - this isn't a concern for me personally, but former playmates have been caught out by this, so be careful if applicable to your situation. Book a room with en suite bathroom that has a bath with shower over it. Some of the cheaper hotels only have a shower, so check first. Stick to messing in the bathroom with the door closed. Check the shower works on arrival. Don't bring anything in tin cans as you might cut yourself. Use the 'do not disturb sign'. Cleanup - aim to pour nearly all the mess down the toilet, flushing periodically. Only the final rinse of the bath should go down the plughole. Bring a plastic jug and plenty of wipes, towels and bin bags for clean-up. Don't use the hotel towels for cleanup (remove them from the bathroom while you play). Tied bin bags full of empty containers, used wipes, gunged clothes etc don't need to be smuggled past reception on your way out. They can usually be left at the end of a corridor and the cleaners will take them away. Have fun
Love you, too
