Reaper

When I can't find a bum gun I improvise. Depending on the shower fittings, I often take off the shower head and use that to clean my ass with. Much less risky actually, as I doubt many ppl do that.
 
I usually just press on the outside of my ass and let the water go in, then run to the toilet and dump it there. The only pain is that this needs to be repeated a few times