I bought this oil plug from Amazon for $5. Is a plastic washer OK? Is there a place where I can buy this for cheaper? And lastly, I ordered the AmSoil Flush. How do you use it? I was going to warm up the car, remove the old filter and put on a cheap filter, empty the oil completely, then put the flush through the engine on the top where the oil would normally go and just wait for it to drain while it's unplugged. Is that the right way? Thanks.