Hard to make a long line with 10ft lengths; it would cost more in fittings than new poly, and decades of UV make integrity a concern. Fine for a gravity drain though; you can just tape the joints together. Could be perforated for a crude leach field. Great for protecting shallow electrical lines against physical damage, or placing as a shallow "early warning" above deeper lines. Would be great as sun-heated air convection tubes to keep an
outhouse pit dry and un-smelly. Good size for a
solar water heater setup, or a
solar heating wall in a garage/shed. Fill with linseed oil to soak thin handles on garden tools. Add a plastic foot valve and it might work as a siphon for emptying
water tanks (tricky). Insert a short length in the ground, down to the root zone of a tree for deep and efficient watering.