Deb, when kitchen slideouts first came out over 20 years ago there were some problems with them over time. Several manufacturers used coil springs to pull the free floating gas or water and/or electric lines in when the slide came in. On some RV's the coil spring would stretch if it got caught on anything or sometimes the spring would break or the screws holding it would pull out for one reason or another. Then the line or electric would get pinched and need repair quick.
Most now are done differently with hinged arms etc and very few problems occur then. It was a learning curve. Much depends on the quality or price level of the RV unit as built. Cheapies cut corners because they have to due to their selling price. Moving drains are not cool and are asking for problems as the RV ages. Drain lines are usually quite large in dia as a small flexible tube drain form a sink wouldn't be good. I'd sure inspect a perspective RV anyway for lots of design or incondition issues before I'd bid on it!