Are you transferring into a vacuum receiver? Photo's of your setup would help. One thing nice about vacuum for transfer of solutions is there is much less stress from pulsing usually encountered with pumps. Aqua regia will leach the plasticizers out of plastic and cause them to become brittle and fail, as will nitric acid.
I prefer to always chill the aqua regia before transfer. I do this for 2 reasons, first the chilled acid is much less aggressive on the tubing, and second, the silver you have to filter out before the next step is much less soluble in a cold aqua regia solution resulting in a higher quality end product.
HDPE exhibits excellent resistance to the effects of the acid, I have found it to be quite expensive. The tubing is also has a tendency to kink which can block flow. The thinner wall tubing is more flexible but it is pretty thin, as the wall thickness increases, the flexibility is pretty poor. I like to use flexible PVC pipe.
http://www.flexiblepvc.net/Flexible_PVC_Pipe_s/23.htm This stuff will degrade from acid exposure but it becomes noticeably more brittle before it fails so need for replacement is easy to recognize. It takes all standard PVC fittings so it is easy to adapt to vacuum tubes or filter fittings and it stands up to vacuum well without collapse. (Thin HDPE does not) One good thing about vacuum transfer is that the hose has to hold vacuum and hose that is about to fail will become brittle often losing its ability to hold vacuum. Plus it fails by sucking air in not squirting acid out.
A fact of life with any production refining operation is routine maintenance, there is no equipment that will last very long without it.
