Pentacta anceps?
It will climb on the wall and sit all the time on the top, facing flow - if the place is inconvenient to you, you can move flow, but cucumber will be persistent.
Try to feed at least few times a day - when the food is long time absent in water column, it closes, and you will not see the luxurious crown of tentacles. Incredible finesse!
Food: see for yourself - it should stick to the tentacles, and will be licked by cucumber, every few seconds or so.
Offer variety, but watch for the reaction - if closes or stops the licking - try something else.
I gave small zooplankton and phytoplankton, plus ZoPlan, Cyclop-eeze (likely too big, but i had other tank inhabitants, who used it), smallest particles after washing frozen cubes (mysis, marine cuisine).
You shouldn't have problems with powerheads or filters intakes, once it climbs up (unless they are very strong - mine were weak, 150 gph), or with heaters. But at least for the first days you may try the plastic heater guards. Likely unnecessary, but who knows.
Licking:
In store:
Opening:
Why heater guard (but yellow is sand-sifting):
Position - always facing flow:
Love it!