sudo apt-get install gamin -y
sudo curl -sSL https://install.pi-hole.net | bash

continue with OK, but note the admin password on the last screen.

edit the file /etc/pihole/adlists.list, put your new block lists there, save and exit.
Then update gravity (pulls in all the domains on the new block lists) with pihole -g
add lists (admin → group management → adlists:

https://firebog.net
https://hosts.oisd.nl
https://github.com/mmotti/pihole-regex/blob/master/regex.list

Test

dig @<piholeServerIp> blockedsite.com

Flush dns

sudo systemd-resolve --flush-caches # Ubuntu
ipconfig /flushdns # Windows

Blacklist – regex blocks

Youtube ads: .*sn-\S{4,}-\S{4,}\.googlevideo\.com
Youtube.com: (\.|^)(youtu\.?be.*|googlevideo\.com)$

Change admin password

sudo pihole -a -p

#Regular update fails on synology due to not being able to check disk space, use override option 'do not follow recommendations' instead.
sudo pihole -up
#curl -L https://install.pi-hole.net | bash /dev/stdin --i_do_not_follow_recommendations

#change the webserver port again:
#vi /etc/lighttpd/lighttpd.conf - change the port
#sed -i 's/server.port\(.*\)= 80/server.port\1= 2080/g' /etc/lighttpd/lighttpd.conf

sudo service lighttpd restart
sudo service pihole-FTL restart

#update might require:
cd /etc/.pihole
git pull

to reconfigure pihole's main details, use:

sudo pihole -r
sudo service pihole-FTL restart