After Fingus and Winkle steal a bottle, they can fill it up at the fountain nearby.
Get Water
Have 
Winkle stand to the left of the hole in front of the
statue, then switch to 
Fingus and click the fountain. While
the fountain is spraying water, switch to Winkle and
right-click to display your inventory, choose the bottle, then use it on the
jet of water.
Get a Stone
Next, have Winkle use the bottle on the toad, then click the
stone to pick it up. Then have Fingus use the stone on the
mechanism to the right of the upper-right window of the house.
Make a Ladder
Then switch to Winkle and have him stand beneath the
upper-right window of the house. Switch to Fingus and click
on the rung that came down from the mechanism, then switch to
Winkle and click on the ladder to have him climb it.
Talk to Tazaar
Have Fingus click on the door, then when Tazaar opens the
window, have him talk to the wizard.
Enter the House
Have Winkle click on the chimney to try to climb in. Tazaar
will agree to let you in. Click on the open door to go into Tazaar's House.