Put up the classic sign:
“I don’t swim in your pool,
Don’t poop in my toilet!”
Rent a “Port O Potty”. We have a company called ‘Blow Brothers’ and they drop it off an pick it up after the event. It isn’t that expensive compared to a big plumbing bill.
If your toilets are clogging up on a regular basis, it may be a combination of old pipes and higher quality toilet paper that doesn’t disintegrate in water readily.
I suggest that before the party you change your toilet paper in all your bathrooms to a cheaper brand that breaks up in water easier. Soft-n-Gentle is such a brand.
I live in a house that was built in 1928. I used to use Quilted Northern and had a lot of problems with clogged pipes. After talking to a longtime employee of a local paper mill, I switched to Soft-n-Gentle and haven’t had a problem since. (I suggest folding over double before wiping, though…)
Oh, please use this one! 
ETA: Not this one as in this bathroom, I meant use this* idea* because I find it hilarious.
Good idea. I have been looking for ways to cut costs and this might put a dent in my cashmere budget. I had to switch after finding out lop-eared bunnies don’t flush too well.
I’d be doing this thread a disservice if I didn’t post this very appropriate to the topic **David Sedaris **story: “Big Boy.” (Link goes to Esquire Magazine’s website.)
There’s something just a little off about the toilet at work. All the poo gets flushed, but invariably, just as the flush cycle nears completion, one piece of poo will come back up out of the hole and float to the surface. A second flush will fail to clear it. Same with the third. It’s not unusual for someone to be in there for 20 minutes, flushing up to 60 times to get rid of that one little bit of shit.
By what? dumping on the floor? (I’d surely be tempted :D). I mean, if you gotta go, you gotta go, and no reasonable host would say otherwise.
If the toilet clogs up as consistently as the OP says, chances are it’s one of the less-able low-flow varieties. Our house, built in 1996, has nothing but those. And while sometimes it’s random as to whether it clogs, othertimes it’s clearly tied to overuse of TP.
We “solve” the problem by having plungers in every bathroom.
On the plus side, since it’s low flow, even two successive flushes aren’t enough to cause the floor to get soaked.
Oh - and more specific to the OP: you can’t, really. A discreet note on the tank back saying “sorry, tends to clog”, and make sure there’s a plunger handy. Everyone has to deal with plunging toilets on occasion and nobody will be terribly shocked.
On an ewww note: we were once spending the night at my in-laws’ apartment. Dweezil, about 6 years old, clogged the toilet with about a ton and a half of TP. I left him soaking in the tub, left the toilet “full” for a couple of minutes to give it a chance to soften (sometimes that’s all it takes - things soften enough to go down, and the water level goes down enough so you can re-flush and all is good).
Well, when I stepped out of the room for a minute, my FIL stopped in to check on my son. Saw the unflushed and too-full toilet, and flushed it. :eek::smack:. I had to clean up that godawful mess. :mad:.
Install a sieve or colander in the toilet. Problem solved!
Ever wonder what he want?
Hmmm. I have it on good authority that girls don’t poop.
Just leave a potato masher next to the toilet.
Or a slotted spoon.
This is especially a good idea if the food bring served at the party is one that would normally require such an implement, either for preparation or serving
I don’t normally get invited to those sorts of parties. 
I do hope the OP will check in after the party to let us know how it went.
I mean that we took a dump if we needed to take a dump; he didn’t actually come into the bathroom with us to make sure we didn’t stink up his precious bathroom. 
Do you mean, “How it went down?”
Dear Friends,
My toilet has some flushing problems and tends to get clogged sometimes. Therefore, if you are going to ‘take a shit’, I would very much prefer that you take it with you and not leave it here.
Thanks.
I read the OP pretty carefully, thank you. I can actually, like, read and stuff. She said that TWO bathrooms will be open to ‘the public’. Of these two, one is hers. She says this of this bathoom:
*
I don’t mind people peeing in my toilet, but nervous about people pooping in it. I’m not open-minded to cleaning up about 4 pounds of shit and water from my bathroom floor, if my toilet stops up and overflows.
So, what should I say? *
To which I replied – having ONE PARTICULAR BATHROOM you are worried about ‘since it clogs easily’ is really not a big deal at a party, ESPECIALLY AS YOU HAVE TWO AVAILABLE BATHROOMS. Just keep an eye on it and all will be fine. That’s all.