Gday Pangit,I have 3 comments about your design.

1. It is good practise to restrict the discharge on a centrifugal pump rather than the suction as it can cause cavatation where the impellar vibrates against the outer houseing.

2.With your vent i suggest that you have a pipe on it going outside incase you overfill tank and oil goes over your garage floor.Not a pretty sight.

3.With your 2 44s welded together if you decide to have a sight tube, go for 3/4 clear plastic pipe as the fats tend to not move up the tube as well with 1/2 inch and can give you a false indication on how full your tank is.

regards westwinds.