A tank system may be conventional and fixed, or mobile, such as a fracking fluid or other tank trailer. A drain port thereof is fitted with an adapter connecting a snorkel system to drain liquids from near the top of the liquid level in the tank. A snorkel head at the extreme distal end of a tube near the longitudinal center of the tank is suspended by a system of buoys. A flow field controller plate resists formation of vortices near the snorkel head, so it can operate as near the surface as possible, withdrawing the highest grade oil efficiently. At its exit, the proximal end of the tube drains oil through an inner conduit of an adapter at a penetration in the wall of the tank. The adapter forms an annulus around the inner conduit draining tank bottoms directly from the tank.