Would post nasal drip from allergies and a deviated septum cause constant sticky clear mucus and occasional dark brown mucus with blood in it?

No. Post nasal drip from allergies is common, and it can produce clear mucous. The deviated septum will not produce discharge. Someone should look to see if they can find the source of the bleeding. That is of concern.
Maybe. The clear mucus is certainly consistent with allergic rhinitis. Deviated septum not involved with allergic symptoms. Occasional brown/blood may be small volume nosebleed tinging mucus or signs of sinus infection, both of which may involve the deviated septum to some degree.

Related Questions

I have an untreated deviated septum and post nasal drip has been aggravating my lungs. And causing dark mucus with blood to come up randomly. Why?

Moisture is needed. Everyone has mucous in back of nose. If you are bothered by it it is because it is too thick (dry). Also dry nose will cause it to bleed. Deviated septum may cause turbulent airflow and worsen dryness. Hydrate, use humidifier, nasal saline spray, and you may try Guaifenesin 1200 mg twice daily to take with food and glass of water. Read more...
See E N T doctor. It is important that you should see a board certified e n t doctor, without delay. Let him/her examine you and advise. Read more...