I had this little do-hicky thingy I bought for my Skyline when I owned it, it was like a little tap, with a lock on it, so you take the lock off shift a bit of metal to open the tap and out flowed the oil, it replaced my sump plug and was nice and cheap, $15 if I remember right. I was constantly scraping too because I'd lowered it unbelieveily and stupidly low, but the sump plug tap never got knocked off or let go. Wonder if they make em for my RD28 actually.... I think it was this:
From:
http://fumoto.com.au/