Hp 2500l prints a dark line horizontal down each page. Can we clean drum at home?

A dark line on the hp 2500 series can come from the drum You can't clean it at home), it can come from a toner cartridge, from the fuser unit and from the optics.
Step one - check if the line in all colors, run copy quality check through Menu and diagnostics, if the line is only on one color your problem is the toner cartridge.
Step two - if the line is on all colors, take the drum unit out and look at the drum, if you see the line on the drum you need to replace the drum unit.
Step three - stop a print in during the printing process by turning the printer off, take out the drum and look at the printed paper under the drum, if the printed page is clear of line your problem is in the fuser.
Good luck.