This is a pretty common issue on camper vans and motorhomes, especially where the sink drains through a flexible chute into a waste tank. What usually happens is a mix of soap residue, grease, and sometimes hair builds up in that low-gradient pipe and slowly restricts flow.
I’d personally be cautious with strong chemical drain cleaners in this setup. A lot of RV plumbing uses softer plastics and glued joints, and aggressive chemicals can weaken seals over time or end up sitting in the waste tank causing more issues later.
A safer first approach is warm (not boiling) water mixed with a bit of dishwashing liquid. Pour it through slowly and repeat a few times. If you can, let it sit for 10–15 minutes to soften the blockage. Another good option is enzyme-based drain cleaners, which break down organic buildup without attacking the pipe material.
If you’re considering professional input or want to compare safe methods used in different regions, you might find it useful to check guidance from
Plumber Singapore since they often deal with similar low-access drainage layouts in compact bathroom systems.
If access is limited and rods or wires aren’t an option, a wet/dry vacuum can sometimes work surprisingly well by sealing it at the sink outlet and pulling the blockage back instead of pushing it further down. I’ve seen this work on similar caravan setups where nothing else would reach.
One more thing, if the blockage is recurring, it might be worth checking the pipe run for a slight sag where debris collects, as that’s usually the root cause in these systems.
