Reddit reviews Camco RV Flexible Swivel Stik with Shutoff Valve- Creates Powerful Cleaning Action that Dislodges and Flushes Stubborn Waste Deposits and Combats Odors (40074),55-1/2 in.
We found 3 Reddit comments about Camco RV Flexible Swivel Stik with Shutoff Valve- Creates Powerful Cleaning Action that Dislodges and Flushes Stubborn Waste Deposits and Combats Odors (40074),55-1/2 in.. Here are the top ones, ranked by their Reddit score.
Powerful rotary cleaning action dislodges and flushes the stubborn waste deposits and odor-causing particles left after holding tank is emptiedSolid section including handle measures 24" long; the flexible section measures 34" long with a 2" diameter nozzleFlexible section is perfect for use with holding tanks that are offset from the toiletEasy grip handle with a standard 3/4" female garden hose connection
You can try getting a black water tank wash nozzle and spray it around through the toilet. Amazon link.
One of these, if he doesn't already have one: https://www.amazon.com/Camco-Flexible-Powerful-Dislodges-40074/dp/B0006IX7YC
One of these (link is a clean amazon link to the thing, no affiliate link; here to help, not make a few bucks). Your family member may not know it yet, but they will need one eventually.
We got one when we had an, erm, 'incident' and it not only cleaned our clog but the literal crap and paper still stuck in the nooks and crannies of the plumbing from previous owners...