Weir and plumming help please??

[snaza]

just setting up a new tank and dont understand how to make the plumming for the weir? does anyone have any pics? should the pipe in the weir be a L shaped pipe to let air in? how does the water get through the pipe? do i have to drill holes in the pipe to let air in? does the pipe going into the sump have to be above water level so it falls into the sump?

i have a 90G with a 20G sump/fuge. what size piping should i use and what size return pump?

sorry for the dumb questions

thanks to anyone who can help