Shave your arse for sure - don't wax or use any of that Veet rubbish. Most WGs will expect you to be clean shaven if you seek this service.
Some WGs might also insist on doing a finger test before engaging in anal play so take a bottle of water with you which has one of those little spouts for drinking through. Screw that into your balloon knot and squeeze a quarter of contents up there to flush anything nasty out of your rectum (obviously do this over the loo and not while you're in the shower).
However, pump too much water up there and you'll flood the sigmoid which will create one hell of a mess. If you start to feel stomach cramps then you've gone to far and rimming (along with everything else) will certainly be off the cards until you've done a complete and thorough flush out (with a least a couple of litres of water), otherwise a single unexpected fart could pebble-dash the surrounding area. Might be an idea to practice at home first with this sort of thing. It's certainly not something which should be deployed in the field without prior testing.
If you do the above you'll get top marks for preparation.
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