Where is jailhouse sewers in runescape?

That's will be located down the trapdoors near Draynor bank ( on the way to draynor via lumbridge shortcut ).
The easiest entrance to the Jailhouse Sewers in Runescape can be found above the market stalls, in Draynor. Look for the Exclamation mark on your map (!). Another entrance can be found East of Draynor, near the jailhouse, however the other way is recommended as the Jail Guards here are aggressive towards players.