I have 3 BN Plecos and they spend most of their time on the glass / equipment cleaning of all the algae
Best advice I've had is give 'em cooked, shelled peas! It stops constipation and they go nuts for them. Just boil 'em for a couple of mins, shell the outer caoting and drop 'em in the tank.
Mine scoot all over the place and take no truck from any other fish, especially where peas are concerned. I do have some wood in there, and they do settle on it occasionally. They do like to have a cavey type place to hide in.
They really are great little characters and are probably my favourite fish to watch. But man can they poo!
Me again - cucumber is nice but of little nutritional value. Mine get a mixed bag of whatever I eat really, carrot, brussels sprouts, rocket, peas, courgette - haven't tried broccoli yet. The algae wafers are good for a bit of protein (and I'm sure that they ate up my dead cory a while back) but advice I have had is to not give too much protein as this can bung em up. Good luck
For bigger pieces of veg - par boil them and they'll sink. I used the bits of lead that wrap around aquatic plants to weigh down my cucumber at first but it didn't look too nice so I bought a 'screwcumber' from ebay and that does the job ina more sightly manner. I have been known to use a teaspoon but the missus didn't like that very much