drilling on 5 plan tanik can be done, but gotta be careful since the "glass: is thin.... i use those moulding material for art and craft, make a ring of wall at the place u gonna drill, when wall up, u can pour water in it... now can drill liao... after drilling, before u sillicon add another pcs of acylic as the glass is thin, can crack easilly. i go for at least 20mm pipe for 1000l or 25mm for 2000l, go hardware store to see the pipe size and feel.