How do I tip my weapons with poison?

Have the arrow equipped, use the poison in your potions menu and it will get applied to the arrow.

Note, you have to repeat this for each arrow, so make the shot count.

When you have a weapon equipped, go to the poison you want to use and select it. It should ask if you want to poison said weapon.

I believe you:

Equip the bow and arrows
Click on poison

It will ask if you want to poison the arrows.

thank you very much, IT WORKED! *does happy dance of joy*

^{ummm stupid respose, but does it stay poisoned?}

No. I think they only stay poisoned for one attack, or two if you get the perk. I do believe a bow in the DB questline gives you a permanently poisoned bow.

can you link me info about this bow? I've done the DB quest line twice but i havent found it..

It's actually the bow that gets poisoned, not the arrow.

So you can equip any kind of arrow you're carrying, and make it a poisoned shot.
You can check your weapons-inventory, to be sure...notice the green poison-symbol next to the bow.

If you're bow is enchanted (let's say with fire-damage), the poison will stack, making it a powerfull hit when combining fire-damage with weakness-to-fire poison.