Short term (acute) blockageMost of the time nose block/ "runny" nose is caused by viral infection. 70% chances are viral and since there is no antiviral but the body's immune system to fight it, the remedy is rest +water and avoid diving. It sounds like a bummer but it is the best solution.
After all, equalising will be difficult and also it is beyond cosmetic reason(nasal drooling) that PADI and experts warn against diving in this condition due to the possible damage that may arise in your middle ear ( i know we have two not three ears- i am referring to the inner workings of the ear) Eardrum perforation is common in individuals who take decongestants and then repeatedly force equalisation during dives.
For thick discharge, best to take some mucolytic ( antimucus) and AVOID decongestants all together. Let it thin down, and then consider a decongestant when it is watery.
If it is watery, you can choose to take oral decongestant (i.e clarinase - combo of antihistamine and pseudoephedrine or just plain pseudoephedrine tablets if there is no sneezing)
If the discharge is green or yellow accompanied by fever, most likely it is an nfection of the sinus glands and antibiotics will be needed.
Chronic BlockageFor those with long standing sinusitis aka RESDUNG ( runny nose all the time) best to seek a specialist help to check the nasal passage for polyps ( growth). Most of the time, it is the little growth that cause the long term problem. Ablation ( surgical cutting) is the most effective way- scientifically proven.
Do we wary of the hocus pocus remedy available in the market.
When in doubt always ask your doctor /pharmacist..
Dive Safe

As a conclusion, dont fight the flu or sinusitis by patching a quick fix and continue diving.. know your limitation. Best to let it wear off for safety reasons.
Aikiben
Blowin bubble the RIGHT way