Uniseal® Pipe-to-Tank Seal Black 3"

UNISEAL Flexible Tank Adapter (bulkhead).

Plumbing through tank walls is made much easier and less expensive using a Uniseal ®. Unlike bulkhead fittings, Uniseals can handle slight irregularities or curvatures without leaking.
Feel like rubber, but they are made of DuPont Alcryn ® rated to 40 psi and warrantied for 25 years.