Somewhat odd question.
If I clean my SKS outside with hot water, would there be any adverse effects on my lawn?
I doubt it. When W Germany was unified with E germany, much of the x39 that they inherited was broken down, and the powder was used as fertilizer. That was in an unburned state though of course, and there wouldn't have been much primer residue.
I just point my muzzle down the toilet, and use a funnel to pour a litre or two out of a kettle...
Careful, One day you might crack the bowl from the rapid change in temperature. Nothing like a busted crapper to mess up your day. I use the bathtub.