a couple of thoughts on this one;
- sex doesn't have to be penetrative, there are many many forms of 'having sex'
- its a fallacy that a bottom has to always spend hours preparing before sex; if you have a good diet, don't eat lots of crap, drink plenty of fluids etc, then it doesn't get 'messy'. If you eat lots of crap, drink lots of crap, then you will be filled with lots of crap, then it does get very messy.
i've had many bfs and we've had spontaneous sex lots of times and very rarely has it been messy. With my current bf with whom working from home at times together we've frequently engaged in random sex with no preparation at all and its been fine.
It is possible you may get a trace of something but thats all.
and ultimately gay sex can definitely be messy (as can all penetrative sex) with fluids everywhere etc let alone sh*t on your dick, it kind of comes with the territory to some extent.