@ Bwenyenye
The 'black thing' is called a water sealant. It prevents the penetration of moisture into the connector/connetion point hence slowing the corrosion. It's good to check the status of the connection on the LNB at least once a year. if there there is alot of corrosion aroing the connector/cable,it's good you redo it (DIY). (This is one point where signal losses can occur.
ii) Majority of Newer TVs have 2 RCA Inputs (AV1 & AV2) & a RF. You can connect the dstv RCA out to AV1,the DVD player to RCA 2 while the aerial connection to RF in of TV(You will have to do a search for this if you hadn't).
iii) During rainy seasons,the signals are really interfered. To minimise/get rid of this,ensure you/who ever is doing the installation have peaked/optimized the signal quality [This is Critical] (so that in times if adverse conditions,the excess microwaves/signals can take charge).
-Another way to take care of rainfades,is to use a bigger dish [Not a favourite for many]. The larger the dish the more microwaves it gathers.
- Try to avoid multiple connections/joints if you can. They cause alot of signal losses.
- Re-alignment is neccessary at least once a year (this can be a DIY).
- Enjoy doing it.
Let My Conscience Be Ever Alive.