Natural bath oil?

I am looking for a natural bath oil that doesn't have any added dyes or fragrance. My son has very dry skin and I think that might help.
Also wondering what bath oil does to the plumbing over time?
Would it build up in the pipes and cause troubles?

I have just started putting virgin coconut oil on my daughters dry hair, hoping that will help. Might hlep with the tangles too I hope. But my son seems allergic to it.